Silicone foam, water-based, aerosol composition

ABSTRACT

A composition useful in producing an open-cell, elastomeric silicone foam combines a silicone oil-in-water emulsion, which forms an elastomer upon removal of the water, with an aerosol propellant. When the composition is discharged to atmospheric pressure, a froth is formed. Removing water from the froth yields an open-cell foam. The froth is stabilized by surfactants, thickeners, or froth stabilizers selected from fibers or lauryl alcohol.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to compositions of room temperature curing,elastomeric, silicone water-based emulsions, froth stabilizers, andaerosol propellants packaged under superatmospheric pressure whichconvert to an open-cell foam when released to atmospheric pressure anddried.

2. Background Information

Bengtson, in U.S. Pat. No. 3,830,760, issued Aug. 20, 1974, discloses aprocess for the manufacture of a foamable composition which comprisesforming a mixture of a polymer or polymer precursor, curable on contactwith the atmosphere, and a polymer soluble inert blowing agent underpressure. His broad list of polymers includes silicone. His examplesshow polyurethanes which are mixed and then transferred to aerosolcontainers. Dispensing the ingredients from the container yields a frothwhich then cures from exposure to the atmosphere to produce aclosed-cell foam.

Sands, in patent application Ser. No. 391,899, now U.S. Pat. No.4,473,667, filed June 25, 1982, assigned to the assignee of the instantapplication, discloses a method of producing a silicone elastomericfoam- from an aqueous silicone emulsion suitable to provide anelastomeric product upon removal of the water. He mechanically generatesa stable froth, then removes the water to form a cured elastomeric foam.He teaches drying by placing in an oven or air drying. Lee et al. inU.S. Pat. No. 4,391,765, issued July 5, 1983, teach a simplified methodof manufacturing a silicone elastomeric foam comprising mechanicallygenerating a stable froth of an aqueous emulsion, while addingsurfactant and thickener, then exposing the stable froth to microwaveenergy to remove the water. Johnson, in U.S. Pat. No. 4,391,921, issuedJuly 5, 1983, disclose a method of producing open-cell sponge byfreezing a silicone emulsion, thawing the frozen article, and dryinguntil the water is removed.

Hagen et al. in German OLS No. 2,909,443, published Sept. 18, 1980,disclose a process for preparing a room temperature curing siliconefoam. A one-component silicone material is mixed with a low boilingsolvent and placed in a bag in a pressure package. A surface pressure,acting on the bag, squeezes the mixture out through a valve to form thefoam.

Sattlegger et al. in U.S. Pat. No. 4,229,548, issued Oct. 21, 1980,describe a process of producing a foam. A hydroxyl endblockedpolydiorganosiloxane and silicon-containing crosslinking agent areplaced into the inner container of a two-container pack. The mixture mayalso contain a gas. The inner flexible container is then placed underpressure by pressurizing the space between the inner and outercontainers. Upon opening the valve, the contents form a uniform closedcell foam, which then cures.

SUMMARY OF THE INVENTION

The composition of this invention, when released from an aerosolcontainer, produces an open-cell, elastomeric foam. The composition,comprising silicone oil-in-water emulsion (optionally lauryl alcohol orfibers), which forms an elastomer upon removal of the water, is combinedwith a blowing agent in a closed container. When the contents aredischarged, a froth is formed. Removing the water from the froth givesan elastomeric foam which has open cells.

It is an object of this invention to produce a composition which isstorable in an aerosol container and which, when released from theaerosol container, forms a froth which converts to an open-cell,elastomeric silicone foam upon removal of water.

It is an object of this invention to produce a composition adapted toproduce an open-cell, elastomeric foam, using an aerosol method togenerate a froth, the froth being stabilized by fibers. By usingelectrically conductive fibers, an electrically conductive foam can beproduced.

It is an object of this invention to produce a composition adapted toproduce an elastomeric foam having small, uniform, open cells, using anaerosol method to generate a froth, the froth being stabilized by laurylalcohol.

DESCRIPTION OF THE INVENTION

This invention relates to a composition, under superatmosphericpressure, consisting of a mixture of (A) 100 parts by weight of siliconeemulsion which is an aqueous, oil-in-water emulsion that cures upondrying at ambient temperature to an elastomeric film, the emulsioncomprising silicone polymer, surfactant, water, and optionally filler,curing agent, thickener, or mixtures thereof, the emulsion having asolids content of from 35 to 80 percent by weight, (B) from 0 to 2 partsby weight of lauryl alcohol, (C) from 0 to 10 parts by weight of fibershaving a diameter of from 1 to 10 micrometers and a length of from 30micrometers to 10 millimeters with a length to diameter ratio of greaterthan 10 to 1, and (D) sufficient aerosol propellant selected from thegroup consisting of nitrogen, nitrous oxide, isobutane, propane,dichlorodifluoromethane, trichlorofluoromethane, and mixtures thereof,to convert said composition to a froth when released to atmosphericpressure at 25° C., the froth producing an open-cell, elastomeric foamupon removal of water.

Methods of producing silicone elastomers have been developed which usean oil-in-water emulsion. The oil-in-water emulsion consists ofdispersed particles of an anionically stabilized polydiorganosiloxaneand a continuous phase of water. Several methods have been developed forfurther processing of the basic polydiorganosiloxane emulsion so that itforms an elastomer when the water is removed from it. Theseelastomer-producing emulsions are further modified in the presentinvention by mixing them in an aerosol container with an aerosolpropellant or blowing agent so that a froth is formed when the contentsare released to the atmosphere. The composition in the container isformulated with thickener, surfactant, froth stabilizer, or combinationthereof, so that the froth which is formed upon release from thecontainer is stable; that is, it remains as a froth while the water isremoved. Upon removal of the water from the froth, an open-cell,elastomeric foam results. The open-cell foam produced from thecomposition of this invention is made up of cells resulting fromruptured bubbles, with very thin, partial walls between the cells inrelation to the cell diameter. A majority of the walls between the cellsare broken so that the foam is porous; that is, gases or liquids readilypass through the foam if under slight pressure. The foam has the heatstability and weatherability typically found with silicone elastomers.

The elastomeric polymer which forms the foam of this invention comesfrom the oil-in-water emulsion of (A). Emulsion (A) has to be stable sothat the mixture has a useful shelf life, for example, 1 year. Emulsion(A) has to be convertible to an elastomer upon removal of the water atroom temperature. The emulsion is required to have a solids content offrom 35 to 80 percent by weight for use in this invention. Solidscontent is the percent by weight of non-volatile material remaining in a2 g sample of the emulsion after it has been heated for 1 hour at 150°C. in an air-circulating oven. The sample is in an aluminum foil dish 60mm in diameter and 15 mm deep. A solids content of 35 percent isconsidered the lower limit which can be used because of the excessiveshrinkage of the froth upon drying and the increasing difficulty inproducing a stable froth with emulsions of lower solids content. Theupper limit of the solids content is determined by the requirement of anoil-in-water emulsion. About 20 percent by weight of water is necessaryin order to maintain the emulsion because of the tendency of theemulsion to thicken and/or gel on storage when lower amounts of waterare present.

There are many different types of elastomeric silicone emulsions whichhave the required characteristic so that they can be used as (A). Asilicone emulsion having a dispersed phase of an anionically stabilizedhydroxylated polydiorganosiloxane and a colloidal silica and acontinuous phase of water in which the pH is 9 to 11.5 as described toJohnson et al. in U.S. Pat. No. 4,221,688, issued Sept. 9, 1980, is apreferred emulsion for use in this invention as (A). U.S. Pat. No.4,221,688 is hereby incorporated by reference to disclose the emulsionand method of manufacture of such an emulsion. Hydroxylatedpolydiorganosiloxanes are those which impart elastomeric property to theproduct obtained after removal of the water from the emulsion. Theyshould have a weight average molecular weight of at least 5,000,preferably in a range of 200,000 to 700,000. The organic radicals of thehydroxylated polydiorganosiloxane can be monovalent hydrocarbon radicalscontaining less than seven carbon atoms per radical and2-(perfluoroalkyl)ethyl radicals containing less than seven carbon atomsper radical. The hydroxylated polydiorganosiloxanes preferably containat least 50 percent methyl radicals with polydimethylsiloxane beingpreferred. The hydroxylated polydiorganosiloxanes are preferably thosewhich contain about 2 silicon-bonded hydroxyls per molecule.

The most preferred hydroxylated polydiorganosiloxanes are those preparedby the method of anionic emulsion polymerization described by Findley etal. in the U.S. Pat. No. 3,294,725 which is hereby incorporated byreference to show the methods of polymerization and to show thehydroxylated polydiorganosiloxane in emulsion. Another method ofpreparing hydroxylated polydiorganosiloxane is described by Hyde et al.in U.S. Pat. No. 2,891,920 which is hereby incorporated by reference toshow the hydroxylated polydiorganosiloxanes and their method ofpreparation.

Another emulsion useful as (A) of this invention is described in Saam,U.S. Pat. No. 4,244,849 issued Jan. 13, 1981, hereby incorporated byreference to disclose the emulsion and method of manufacture of such anemulsion. This emulsion comprises a continuous water phase and ananionically stabilized dispersed silicone phase which is a graftcopolymer of a hydroxyl endblocked polydiorganosiloxane and an alkalimetal silicate which is present in the continuous water phase. Theemulsion has a pH within the range from 8.5 to 12 inclusive. Thehydroxyl endblocked polydiorganosiloxane useful in this embodiment isthe same as that described above. The alkali metal silicates that aresuitable are water soluble silicates, preferably employed as an aqueoussolution. Preferred is sodium silicate in an amount of from 0.3 to 30parts by weight for each 100 parts by weight of polydiorganosiloxane.During the preparation of the emulsion an organic tin salt is added tocatalyze the reaction of the hydroxyl endblocked polydiorganosiloxaneand the alkali metal silicate. A diorganotindicarboxylate is a preferredorganic tin salt with from 0.1 to 2 parts by weight employed for each100 parts by weight of polydiorganosiloxane. The preferreddiorganotindicarboxylate is dioctyltindilaurate.

Another emulsion useful as (A) of this invention is described to Willingin U.S. Pat. No. 4,248,751, issued Feb. 3, 1981, hereby incorporated byreference to disclose the emulsion and its method of manufacture. Foruse in this invention, the emulsion includes the addition of colloidalsilica. This emulsion is the emulsion produced by a process comprisingemulsifying (5) a vinyl endblocked polydiorganosiloxane and (6) anorganosilicon compound having silicon-bonded hydrogen atoms using waterand surfactant to form an emulsion, adding a platinum catalyst andheating the emulsion to form a dispersed phase of crosslinked siliconeelastomer, then adding colloidal silica. The vinyl endblockedpolydiorganosiloxane (5) preferably is a polydiorganosiloxane terminatedby triorganosiloxy groups and having two vinyl radicals per molecule, nosilicon atom having more than one vinyl radical bonded thereto. Theremaining organic radicals are preferably those with six carbon atoms orless with the preferred organic radicals being selected from the groupconsisting of methyl, ethyl, phenyl, and 3,3,3-trifluoropropyl radicals,at least 50 percent of the radicals being methyl radicals. Thepolydiorganosiloxane should have a viscosity of from 0.1 to 100 Pa·s at25° C.

In this embodiment, the organosilicon compound (6) is one which containssilicon-bonded hydrogen atoms. This compound can be any compound orcombination of compounds containing silicon-bonded hydrogen atoms usefulas crosslinkers and providing an average of at least 2.1 silicon-bondedhydrogen atoms per molecule of (6) of at least 2.1. Such compounds areknown in the art as illustrated to Polmanteer et al. in U.S. Pat. No.3,697,473, issued Oct. 10, 1972, which is hereby incorporated byreference to show such organosilicon compounds. A preferredorganosilicon compound is a mixture which consists essentially of (a) anorganosiloxane compound containing two silicon-bonded hydrogen atoms permolecule and the organic radicals being selected from the groupconsisting of alkyl radicals having from 1 to 12 carbon atoms inclusive,phenyl, and 3,3,3-trifluoropropyl radicals, no silicon atom havingbonded thereto more than one silicon-bonded hydrogen atom, and saidorganosiloxane (a) having no more than 500 silicon atoms per molecule,and (b) an organosiloxane compound containing at least 3 silicon-bondedhydrogen atoms per molecule, the organic radicals being selected fromthe group defined above for R', no silicon atom having bonded theretomore than one silicon-bonded hydrogen atom and said organosiloxanecompound (b) having no more than 75 silicon atoms per molecule. Thismixture is such that at least 10 percent of the silicon-bonded hydrogenatoms are derived from (a) or (b) and the combination of (a) and (b)provides 100 weight percent of the mixture. The organosilicon compoundis preferably added in an amount such that there are present from 0.75to 1.50 silicon-bonded hydrogen atoms in the compound (6) for each vinylradical in the vinyl endblocked polydiorganosiloxane (5).

Another emulsion useful in part (A) of this invention is described toSaam et al. in U.S. Pat. No. 4,273,634, issued June 16, 1981, which ishereby incorporated by reference to show the emulsion and method ofmanufacture of an emulsion useful in this invention when colloidalsilica is also present in the emulsion. The emulsion of this embodimentcomprises an emulsion prepared by first forming a stabilized dispersionof hydroxyl endblocked polydiorganosiloxane containing sufficient vinylsubstituted siloxane units to facilitate the crosslinking of thepolydiorganosiloxane and having a weight average molecular weight of atleast 5000. The preferred weight average molecular weight is in therange of from 200,000 to 700,000. The organic radicals of the hydroxylendblocked polydiorganosiloxane can be monovalent hydrocarbon radicalscontaining less than seven carbon atoms per radical and2-(perfluoroalkyl)ethyl radicals containing less than seven carbon atomsper radical. It is preferred that at least 50 percent of the radicalsare methyl radicals with a preferred polydiorganosiloxane being acopolymer containing dimethylsiloxane units and methylvinylsiloxaneunits. The amount of vinyl-substituted siloxane units is not critical,typically about 0.03 to 0.06 mole percent of the vinyl-substitutedsiloxane units are preferred.

A preferred method of forming the stabilized dispersion is to preparethe polydiorganosiloxane by emulsion polymerization, preferably by themethod of U.S. Pat. No. 3,294,725 cited above.

After the dispersion of hydroxyl endblocked polydiorganosiloxanecontaining vinyl substituted siloxane units has been made, it is treatedto provide a crosslinking action by forming free radicals within thedispersed polydiorganosiloxane. Any of the methods known in the art toproduce free radicals that will crosslink the polydiorganosiloxane canbe employed in the present invention as long as the free radicals can begenerated within the dispersed particles without breaking or coagulatingthe dispersion. Generally, crosslink-inducing radicals can be producedby energy activation of the polydiorganosiloxane directly or by energyactivation of radical-producing agents dissolved in the droplets.

After the polydiorganosiloxane in the emulsion is crosslinked, colloidalsilica is added to the emulsion, preferably in the form of an aqueousdispersion of colloidal silica. The amount of colloidal silica is notcritical, up to 70 parts can be added with a preferred amount from about10 to 25 parts by weight of colloidal silica per 100 parts by weight ofpolydiorganosiloxane.

Another emulsion useful in (A) of this invention is described in thepatent application, Serial No. 624,545, titled "PolydiorganosiloxaneLatex", by Huebner and Saam, filed on June 25, 1984, and having the sameassignee, which is hereby incorporated by reference to describe theemulsion and its method of manufacture. In this method of producing anaqueous emulsion of crosslinked polydiorganosiloxane, a hydroxylendblocked polydiorganosiloxane is mixed with a hydrolyzable silanehaving 3 or 4 hydrolyzable groups, a surface active anionic catalystselected from the group consisting of a compound of the formula R'C₆ H₄SO₃ H wherein R' is a monovalent aliphatic hydrocarbon radical of atleast 6 carbon atoms and a compound of the formula R'OSO₂ OH wherein R'is as defined above, and sufficient water to form an oil-in-wateremulsion. The mixture is immediately homogenized, then allowed topolymerize at a temperature of from about 15 to 30° C for at least 5hours at a pH of less than 5 until a crosslinked polymer is formed. Thecrosslinked polymer emulsion is then neutralized to a pH of greater than7 and reinforced by adding greater than 1 part by weight of colloidalsilica sol or silsesquioxane.

At the present time, it is considered that stable, silicone oil-in-wateremulsions which are convertible to an elastomer upon removal of thewater at room temperature, and which have the required solids content,are suitable for use in the method of this invention.

The composition of this invention, consisting of a mixture of (A), (B),(C), and (D), must form a froth when it is released to atmosphericpressure. A froth is defined as a structure that will maintain its shapeand does not collapse upon removal of water. A froth that will maintainits shape is obtained by use of froth stabilizers in the composition,such as additional surfactant, thickener, fibers, lauryl alcohol, ormixtures of these froth stabilizers. Preferred surfactants includeanionic surfactants such as the salt of the surface active sulfonicacids used in the emulsion polymerization to form the hydroxylendblocked polydiorganosiloxanes as shown in U.S. Pat. No. 3,294,725cited above which is hereby incorporated by reference to show thesurface active sulfonic acids and salts thereof. The alkali metal saltsof the sulfonic acids are preferred, particularly the sodium salts. Thesulfonic acid can be illustrated by aliphatically substitutedbenzenesulfonic acids, aliphatically substituted naphthalene sulfonicacids, aliphatic sulfonic acids, silylalkylsulfonic acids, andaliphatically substituted diphenylether sulfonic acids. Other anionicemulsifying agents can be used, for example, alkali metalsulforicinaleates, sulfonated glyceryl esters of fatty acids, salts ofsulfonated monovalent alcohol esters, amides of amino sulfonic acidssuch as the sodium salt of oleyl methyl tauride, sulfonated aromatichydrocarbon alkali salts such as sodium alpha-naphthalene monosulfonate,condensation products of naphthalene sulfonic acids with formaldehyde,and sulfates such as ammonium lauryl sulfate, triethanol amine laurylsulfate, and sodium lauryl ether sulfate.

The froth can also be stabilized with nonionic emulsifying agents inaddition to the anionic emulsifying agents. Such nonionic emulsifyingagents can be illustrated by saponins, condensation products of fattyacids with ethylene oxide such as dodecyl ether of tetraethylene oxide,condensation products of ethylene oxide and sorbitan trioleate,condensation products of phenolic compounds having side chains withethylene oxide such as condensation products of ethylene oxide withisododecylphenol, and imine derivatives such as polymerized ethyleneimine.

The froth can be stabilized by thickening agents, suitable thickenersare commercially available and would be selected for their stability andusability in thickening the emulsion at the pH of the emulsion beingused. Some of the useful thickeners include the classes of cellulosederivatives, alkali salts of polyacrylates and polymethacrylates, sodiumand ammonium salts of carboxylate copolymers, and colloidal clays. Theseand other thickeners can be used, but it is advisable that a particularthickener be tried on a small scale to determine that it does notadversely effect the storage stability of the emulsion or the resultingproperties of the elastomeric foam.

A particularly useful method of stabilizing the froth is through the useof fibers as a froth stabilizer. The fibers used are fibers which arenot adversely effected by the aqueous emulsions, many of which arestrongly alkaline. The fibers are more successfully dispersed into theemulsion (A) if their average diameter is less than 10 micrometers andtheir length is less than 10 mm, preferable the diameter is less than 5micrometers and the length is less than 8 mm. The smaller the diameterof the fibers and the shorter they are, the easier they are to disperse.Glass fibers having a diameter of about 3 micrometers and an averagelength of about 4 mm are preferred. The minimum diameter of usefulfibers is about 1 micrometre and the minimum length of useful fibers isabout 20 micrometres. The fibers must be dispersed in the emulsion inorder to be able to dispense the composition from a container withoutclogging the valve when the composition is dispensed from an aerosolcontainer through a valve. Electrically conductive foams have beenproduced using graphite fibers and graphite fibers coated with nickel.Fibers which are ductile, rather than brittle like the glass or graphitefibers, have also been used. Stainless steel fibers are more difficultto disperse without clumping than are glass fibers. The ductile fibersbend rather than break during the mixing and dispersion step. The bentfibers tend to become hooked together into clumps which clog the valve.Mixtures of fibers can also be used.

The amount of fibers required to obtain a froth is dependent upon theemulsion (A) that is used as well as the use of any other frothstabilizers in conjunction with the fibers. A range of from 1 to 10parts by weight of fibers may be necessary to provide froth where thefibers are the only froth stabilizer. A preferred range is from 2 to 5parts by weight of fibers per 100 parts by weight of emulsion (A).

It is believed that the fibers act as a froth stabilizer in that theyreinforce the walls of the cells as the froth is formed. The reinforcedcell walls do not collapse as the froth is dried so that a foam isformed by drying the stabilized froth. The fibers also act as areinforcement in the foam cell walls so that the foam is stiffer andtougher than when fibers are not present. Foams produced with fibers asa froth stabilizer have improved tear strength over those not containingfibers.

A particularly soft and uniformly small cell foam is produced whenlauryl alcohol is used as the froth stabilizer in an amount of from 0.1to 2 parts by weight. Lauryl alcohol is preferably added to emulsion (A)in amounts between 0.2 to 1.5 parts by weight per 100 parts of emulsion(A). This addition thickens the emulsion and stabilizes the frothproduced when the mixture is dispersed. Lauryl alcohol has been found tobe unique in its ability to produce a froth of uniform, small cells, theindividual cells having diameters of about 0.2 to 0.3 mm diameter,whereas foams produced with similar formulations but without the laurylalcohol have cells varying from 0.10 to 1.5 mm in diameter. The laurylalcohol produces a froth which does not shrink excessively as it isdried to produce foam. The foam produced has a smoother outer surfacethan is produced without the lauryl alcohol. The foam is softer whenmade with the lauryl alcohol than when made without it. Preferred foamsmade containing lauryl alcohol have cells with diameters of from 0.2 to0.3 mm, have greater than 30 cells per linear cm, and have a density ofless than 200 kg/m³.

Foam can be produced using mixtures of the surfactants, thickeners, andfroth stabilizers as desired to obtain different characteristics in thefinished foam. For example, a foam can contain both surfactant andlauryl alcohol or surfactant and electrically conductive fibers, orglass fibers and lauryl alcohol. A preferred combination is from 0.2 to1.5 parts by weight of lauryl alcohol and from 2 to 5 parts by weight ofglass fibers having a diameter of less than 5 micrometers and an averagelength of less than 5 mm. By using fibers and/or lauryl alcohol as frothstabilizer, a very stable froth can be produced. Because of this frothstability, the amount of blowing agent used can be in the upper portionof the useful range, resulting in more expansion of the froth and alower density foam after removal of the water from the froth. If amountsof blowing agent in the upper portion of the useful range are added toemulsions which do not contain the fibers or lauryl alcohol as frothstabilizer, the froth may expand to a point where it collapses becausethe cell walls are not stable enough to resist the larger amount ofexpansion.

The composition, in a container under superatmospheric pressure, istransformed into a froth, when released to atmospheric pressure, by theaerosol propellant (D) that is present in the composition. The aerosolpropellant is a substance that is soluble or dispersible in the mixturewhile it is in the closed container and which is a gas upon release fromthe closed container into the atmosphere. Superatmospheric pressure isdefined as pressure above atmospheric pressure sufficient to contain thecomposition. Aerosol propellants are well-known in the art. They can bea gas such as nitrogen or nitrous oxide which is under pressure in thecan and dispersed through the composition, which then expands themixture into a froth when the mixture is released into the atmosphere.They can be a material such as isobutane, propane,dichlorodifluoromethane, or trichlorofluoromethane which are liquidswhile in a closed container under pressure, then expand into a gas whenreleased into the atmosphere. Mixtures of aerosol propellants can alsobe used in the composition to obtain the desired amount of frothing whenthe mixture is released to the atmosphere. Aerosol propellants arematerials which are liquid or gas under pressure and become gas atatmospheric pressure and ambient temperatures. Useful materials that areliquids under pressure are those which can be liquified at ambienttemperature under pressures of less than about 1 megapascal (1.034MPa=150 psi) because this is a practical, safe upper-pressure limit.Preferred propellants for use in this invention include the hydrocarbonssuch as isobutane and propane, and the chlorofluorocarbons such asdichlorodifluoromethane and trichlorofluoromethane. Because somepropellants such as difluoroethane, difluorochloromethane anddimethylether were found to be unsatisfactory when used by themselves asblowing agents, it is recommended that the blowing agent used be testedfor compatibility with the emulsion (A) and froth stabilizer being usedin the composition. Another type of propellant which can be used aregases such as nitrogen, nitrous oxide, air, argon, and helium, which areused to pressurize the container without becoming liquified. Nitrogenand nitrous oxide are preferred because they are inert to the mixtureand to the container. Air and oxygen can be used if the metal can isprotected from oxidation. Carbon dioxide is not acceptable as apropellant because it causes coagulation of the emulsion (A). Compressedgases are used in sufficient amount to give a pressure of from 0.15 to1.0 megapascal. The compressed gases are not the preferred propellantsbecause the pressure in the container drops as the contents areexpelled; therefore, the degree of frothing changes as the contents ofthe container are discharged. The preferred propellant is from 1 to 20parts by weight of propane, isobutane, or mixture of propane andisobutane with the most preferred amount from 1.5 to 8. A preferredcomposition uses a combination of from 0.2 to 1.5 parts by weight oflauryl alcohol and from 1.5 to 8 parts by weight of these preferredpropellants. In general, as more propellant is added, the more themixture froths when released from the closed container. If too muchpropellant is added, the mixture froths too much and the froth is notstable, that is, the froth collapses, either immediately or as the wateris removed.

The composition of this invention produces an open-cell, elastomericfoam by removing the water from the froth. The froth is obtained bydispensing the composition from a closed container having an outletvalve, the composition being under pressure greater than atmosphericwhile in the container. The composition of the mixture is such that asthe mixture is released from the closed container, the mixture expandsto form a froth. This composition consists of a mixture of the siliconeoil-in-water emulsion discussed above, a propellant discussed above, andoptionally, a froth stabilizer as discussed above.

The closed container can be a one-compartment or two-compartment aerosolcan such as is well-known in the industry. The outlet valve on theaerosol can is preferably of the type known as a "toggle action" valve.In a one-compartment can, the contents are discharged by turning the canover so that the valve is on the bottom, then opening the valve. Becausethe viscosity of the mixture in the can is relatively high, this type ofvalve, which does not use a dip tube, is preferred. With theone-compartment can, the contents of the can are forced out by thepressure exerted by the propellant, which also acts as a blowing agentin this case. In a two-compartment piston type can, the composition isforced out by the propellant in the lower compartment of the can. Thecomposition in the upper part of the can contains propellant which actsas a blowing agent to produce the froth upon release to atmosphericpressure. In some cases, a two-compartment can is desirable because theblowing agent type and amount can be selected to obtain the preferredrate and amount of froth generated while the propellant can beindependently selected to produce the preferred pressure inside the can.In a one-compartment can, the blowing agent and propellant are the sameso that there is a relationship between the pressure in the can whichforces the mixture out and the pressure which forms the froth.

The emulsion (A) which is used in this invention is selected from thosediscussed above to produce the type of elastomeric foam preferred by theuser. In general, an emulsion with a higher viscosity produces a morestable froth. The stability of the froth can be adjusted by the amountof surfactants and/or thickeners present in the emulsion as discussedabove. In addition, a froth stabilizer as discussed above can be added.

In a one-compartment aerosol can, the mixture of emulsion and frothstabilizer is placed into the closed container and the outlet valve iscrimped in place. A propellant is added to the mixture through theoutlet valve or under the valve just prior to crimping, using equipmentwell-known in the aerosol industry. The container is then placed on ashaker or similar device to mix and disperse the propellant into therest of the mixture. The propellant also serves as blowing agent.

In a two-compartment piston type can, the mixture of emulsion and frothstabilizer is placed into the inner compartment and the outlet valve iscrimped into place. A blowing agent is added to the mixture through theoutlet valve or under the valve just prior to crimping. A propellant isthen placed in the outer compartment of the can. The propellant in theouter compartment must be at a higher pressure than the blowing agent inthe inner compartment because the purpose of the propellant is forcingthe contents from the can. The two compartment can allows differentmaterials to be used for the blowing agent and the propellant, whereasthe one-compartment can requires one material to perform both functions.

After the mixture is prepared in the can, a froth is formed bydispensing the mixture from the can into a space at atmosphericpressure. The mixture is forced out of the can through the outlet valvebecause of the pressure from the propellant in the can. The mixture willexit the valve as a liquid which is then expanded into a froth by theblowing agent in the mixture. The expansion can take place slowly if themixture is of a high viscosity and the blowing agent selected is onewith a low vapor pressure. The rate of expansion of a particular mixturecan be increased by lowering the viscosity of the mixture, using ahigher vapor pressure blowing agent, or using additional blowing agent.Preferably, the ingredients are chosen so that the mixture forms a frothimmediately because the amount of froth being produced is easilyobserved and the valve can be shut when the desired amount of froth ispresent. If the froth is formed more slowly, it is more difficult tojudge how long the valve should be open in order to obtain a desiredamount of froth.

The composition can be dispensed onto a surface and allowed to frothfreely or it can be dispensed into a space, for instance a crack or amold, and allowed to fill the space in the crack or assume the shape ofthe mold. The froth maintains its existence as a froth while the wateris removed to produce an open-cell, elastomeric foam.

The water can be removed from the froth by exposing the froth to ambientconditions and allowing the water to evaporate. This simple method ofremoving the water allows the composition to be used as a foam sealantto fill cracks in a building, for example. Other methods of removingwater, such as exposure to heated air, can also be used.

A composition of this invention comprising (A), from 0.2 to 2 parts byweight of lauryl alcohol, and (C), without (D) present as it is in thecomposition of claim 1, is a stable emulsion which is a usefulintermediate in manufacturing silicone foam. Such a compositioncomprises those ingredients which are mixed and placed into an aerosolcontainer such as described above. The propellant (D) is then introducedinto the container under pressure. Such a composition is also useful ina continuous production process. In such a process, this composition isfed into a mixing chamber at a controlled rate. A propellant is also fedinto the mixing chamber at the required rate to give the correct ratiofor producing the froth. The mixture of this composition and propellantis then continuously discharged from the mixing chamber to form thefroth. The froth is dried to produce silicone foam on a continuousbasis.

The composition of this invention produces open-cell, elastomeric foam.Because the foam is based upon elastomeric silicone polymers, the foampossesses good heat stability and weatherability when compared toorganic based foams. The foam is useful as insulation, lightweight gapfiller, and as lightweight sealant. If the known fire retardantadditives such as carbon black and platinum are added to thecomposition, the foam can be made more fire resistant. The foam can bemade electrically conductive by addition of carbon black and/or otherelectrically conductive fillers, including conductive fibers asdiscussed above, and used as electrical connectors or pressure switches.

The following examples are included for illustrative purposes and shouldnot be construed as limiting the scope of the invention which isproperly delineated in the claims. Amounts given as parts or percent areparts by weight or percent by weight.

EXAMPLE 1

A silicone foam, using an aerosol method of producing the froth, wasprepared in which the froth was dried at room temperature.

An aqueous silicone emulsion which formed an elastomer upon removal ofthe water was prepared from 100 parts of an emulsion of hydroxylendblocked polydimethylsiloxane prepared by anionic emulsionpolymerization and having 58 percent polymer in the emulsion, 58 partsof a colloidal silica sol having 15 percent of silica and a pH of about10, 0.28 part of an emulsion of dibutyltindilaurate having 50 percent ofthe tin compound, diethylamine, and acrylic thickener. This emulsion(Emulsion A) had about 42 percent by weight solids content, a pH ofabout 11, a viscosity of about 20 Pa·s at 25° C., and produced asilicone elastomer when the water was removed from the emulsion at roomtemperature.

The upper portion of a two-compartment aerosol can was filled with 45 gof Emulsion A and 3 g of a 35 percent solution of disodium N-octyldecylsulfosuccinamate surfactant, and 4 ml of isobutane (specific gravity of0.599) as blowing agent (100 parts Emulsion A, 2.3 parts surfactant, 5.3parts blowing agent). The lower portion of the can was filled with about15 ml of a mixture of 80 percent by weight isobutane and 20 percent byweight propane, as the propellant.

After the can was shaken to thoroughly mix the contents, the valve wasopened and the contents discharged as a froth onto a surface. The frothslowly continued to expand for about 1 hour until the outer surfaceformed a skin. The froth was allowed to dry at room temperature. Thecured foam was open-celled, and had a density of about 109 kg/m³.

EXAMPLE 2

A series of compositions containing lauryl alcohol as a froth stabilizerwere prepared and placed in aerosol cans for evaluation in making foam.

Emulsions were prepared by mixing together 160 g of Emulsion A, 9 g ofthe surfactant used in Example 1, and the amount of lauryl alcohol shownin Table I. The viscosity of each mixture was measured with the resultshown in Table I. Each of these emulsions were then poured into aone-compartment aerosol can and a valve, "toggle action" type, wassealed onto the can. The can was then charged with the amount ofpropellant shown in Table I. The contents were shaken thoroughly to mix,then the contents were discharged onto aluminum panels as strips offroth and allowed to dry for about 24 hours to form open-celled foam.The foam density and cell size were then measured with the results shownin Table I. The density was determined by cutting small cubes from thefoam, weighing them, measuring their size, and then calculating thedensity. The densities shown are values obtained by averaging variousvalues obtained at different points in the sample. The densities variedabout plus or minus 8 kg/m³ from the average.

The foam made containing lauryl alcohol had smaller, more uniform cellsthan the foam not containing lauryl alcohol. The foam containing laurylalcohol was much softer and elastic than the foam not containing thelauryl alcohol. The foam containing lauryl alcohol maintained fullexpansion during drying with less collapse than the foam not containinglauryl alcohol.

                  TABLE I                                                         ______________________________________                                        Composition                                                                   Lauryl                   Foam Properties                                      Alcohol                                                                              Viscosity                                                                              Propellant   Density  Cell Size                               g      Pa · s                                                                        kind    ml  Parts                                                                              kg/m.sup.3                                                                             mm                                  ______________________________________                                        none   10.5     A-31    3   1.1  137      0.15-1.5                            none   10.5     A-31    6   2.2  Collapsed                                    0.3    11.0     A-70    5   1.8  64       0.2-0.3                             0.9    14.6     A-70    5   1.8  35       0.2-0.3                             2.1    38.4     A-31    3   1.1  105      0.2-0.3                             2.1    38.4     A-31    6   2.2  39       0.2-0.3                             ______________________________________                                         A-31 is isobutane                                                             A70 is a 50/50 by volume mixture of isobutane and propane.               

EXAMPLE 3

A variety of alcohols were evaluated for use as froth stabilizers.

A series of compositions were mixed and placed into aerosol containersas in Example 2 using 45 g of Emulsion A, 3 g of the surfactant ofExample 1, 0.2 g of the alcohol shown in Table II and 2 ml of isobutanepropellant (100 parts Emulsion A, 2.3 parts surfactant, 0.4 partsalcohol, 2.7 parts propellant). After thorough mixing, the samples weredischarged, dried, and evaluated as in Example 2 with the results shownin Table II.

Lauryl alcohol was the only alcohol which was a useful froth stabilizerin that it gave a uniform, small-celled foam with a smooth, uniformsurface on the foam. The other alcohols yielded foams which werecollapsed with rough irregular surfaces.

                  TABLE II                                                        ______________________________________                                                    Density   Cell Size                                               Alcohol     kg/m.sup.3                                                                              mm       Appearance                                     ______________________________________                                        lauryl  (C.sub.12)                                                                            48        0.2-0.3                                                                              A                                            1-propyl                                                                              (C.sub.3)*                                                                            74        0.5-2.0                                                                              D                                            octyl   (C.sub.8)*                                                                            101       0.5-2.0                                                                              D                                            decyl   (C.sub.10)*                                                                           97        0.5-2.0                                                                              D                                            tridecyl                                                                              (C.sub.13)*                                                                           166       0.5-2.0                                                                              D                                            furfuryl                                                                              (a)*    72        0.5-2.0                                                                              D                                            benzyl  (b)*    95        0.5-2.0                                                                              D                                            ______________________________________                                         ##STR1##                                                                      ##STR2##                                                                      A is no collapse, smooth surface                                              D is partial or complete collapse, rough irregular surface                    *Comparative Examples                                                    

EXAMPLE 4

Foam was prepared using glass fibers as the froth stabilizer.

A composition was prepared by mixing 43.7 g of Emulsion A with 1.3 g ofglass fibers in a mixer until the glass fibers were dispersed throughoutthe emulsion (100 parts Emulsion A and 3 parts glass fibers). The glassfibers had diameters ranging from 2.6 to 3.8 micrometers and lengths ofless than 8 mm with an average of about 4 mm. The composition was thenplaced in the upper portion of a two-compartment aerosol can, a valveapplied, and 2 ml (2.7 parts) of isobutane added as blowing agent. Thepropellant in the lower portion of the can was 5 ml of the mixture ofisobutane and propane used in Example 1.

After mixing, the contents were discharged as a frorh onto a surface.The froth was stabilized by the glass fibers and did not collapse duringthe drying period at room temperature. After drying, an open-cell foamhaving walls reinforced with the glass fibers resulted. The foam had adensity of about 330 kg/m³ with comparatively large, cells. The foam wastougher and less compressible than a similar foam made without the glassfibers, using lauryl alcohol to stabilize the froth.

A comparative example was prepared as above, but the glass fibers werenot added to the composition. When discharged from the aerosol, thecomposition formed a froth, but the froth was not stable. The frothcollapsed on standing and the emulsion dried as a flat film rather thanas a foam.

EXAMPLE 5

A foam was prepared using both glass fibers and lauryl alcohol as frothstabilizers.

A composition was prepared by mixing 43.7 g of Emulsion A with 1.3 g ofthe glass fibers of Example 4, 4.5 g of sodium lauryl sulfate surfactantas a 30 percent by weight solution in water, and 0.3 g of lauryl alcohol(100 parts Emulsion A, 3 parts glass fibers, 0.7 part lauryl alcohol, 10parts surfactant). After mixing, the composition was placed in anaerosol one-compartment can, the valve applied, and 4 ml (5.5 parts) ofisobutane were added as blowing agent and propellant. After mixing, thecontents were discharged as a froth onto a surface. The froth, beingstabilized by both the glass fibers and lauryl alcohol was very stableand did not collapse. It expanded to a greater extent than in Example 4because a higher concentration of the blowing agent was present and thefroth stabilizers maintained the structure during drying. The foamobtained upon removing the water from the froth by drying at roomtemperature had a density of 86 kg/m³.

EXAMPLE 6

An electrically conductive foam was prepared by using nickel-coatedgraphite fibers as the froth stabilizer.

A composition was prepared by mixing 92.2 g of Emulsion A, 9.8 g ofsodium lauryl sulfate surfactant, 2.8 g of nickel-coated graphitefibers, and 14.5 g of lampblack (100 parts Emulsion B, 10.6 partssurfactant, 3 parts fibers, 16 parts lampblack). The fibers had anominal diameter of 8 micrometers and were about 3 mm in length. Thecomposition was placed in an aerosol one-compartment can and a valveapplied. The can was charged with 3 ml (1.9 parts) of isobutane asblowing agent and propellant.

The contents were discharged, after mixing, onto a surface as a froth.The froth was dried at room temperature to remove the water and form anopen-cell foam. The foam had a surface resistivity of approximately 60ohms per square.

EXAMPLE 7

A sample was prepared using nitrogen as the blowing agent andpropellant.

A composition was prepared by mixing 100 g of Emulsion A, 5 g of thesurfactant of Example 2 and 0.6 g of lauryl alcohol (100 parts EmulsionA, 5 parts surfactant, 0.6 part lauryl alcohol). After mixing, thecomposition was placed in an aerosol can, a valve attached, and theone-compartment can was charged with nitrogen at a pressure of 859 kPa.

The contents were charged onto a surface as a froth. The froth was driedat room temperature to remove the water and form an open-cell foam. Thefoam had a density of 112 kg/m³ with small, uniform cells of about 0.2to 0.3 mm diameter.

That which is claimed is:
 1. A composition, under superatmosphericpressure, consisting of a mixture of(A) 100 parts by weight of siliconeemulsion which is an aqueous, oil-in-water emulsion that cures upondrying at ambient temperature to an elastomeric film, the emulsioncomprising crosslinked silicone polymer, surfactant, water, andoptionally filler, curing agent, thickener, or mixtures thereof, theemulsion having a solids content of from 35 to 80 percent by weight, (B)from 0 to 2 parts by weight of lauryl alcohol, (C) from 0 to 10 parts byweight of fibers having a diameter of from 1 to 10 micrometers and alength of from 30 micrometers to 10 millimeters with a length todiameter ratio of greater than 10 to 1, and (D) sufficient aerosolpropellant selected from the group consisting of nitrogen, nitrousoxide, isobutane, propane, dichlorodifluoromethanetrichlorofluoromethane, and mixtures thereof, to convert saidcomposition to a froth when released to atmospheric pressure at 25° C.,the froth producing an open-cell, elastomeric foam upon removal ofwater.
 2. The composition of claim 1 in which (B) and (C) are zero. 3.The composition of claim 1 in which (B) is from 0.2 to 1.5 parts byweight.
 4. The composition of claim 1 in which (C) is from 1 to 10 partsby weight.
 5. The composition of claim 3 in which (C) is zero.
 6. Thecomposition of claim 4 in which (B) is zero.
 7. The composition of claim4 in which the fibers are glass fibers having a diameter of less than 5micrometers and an average length of less than 8 millimeters.
 8. Thecomposition of claim 4 in which the fibers are electrically conductive.9. The composition of claim 8 in which the electrically conductivefibers are nickel-coated graphite.
 10. The composition of claim 1 inwhich (B) is from 0.2 to 1.5 parts by weight and (C) is from 2 to 5parts by weight of glass fibers having a diameter of less than 5micrometers and an average length of less than 5 millimeters.
 11. Thecomposition of claim 1 in which (D) is from 1 to 20 parts by weight ofpropane, isobutane, or mixture of propane and isobutane.
 12. Thecomposition of claim 1 in which (D) is sufficient nitrogen or nitrousoxide to give a pressure of from 0.15 to 1.0 megapascal.
 13. Thecomposition of claim 5 in which (B) is from 0.2 to 1.5 parts by weightand (D) is from 1.5 to 8 parts by weight of propane, isobutane, ormixture of propane and isobutane.
 14. A composition consisting of(A) 100parts by weight of silicone emulsion which is an aqueous, oil-in-wateremulsion that cures upon drying at ambient temperature to an elastomericfilm, the emulsion comprising crosslinked silicone polymer, surfactant,water, and optionally filler, curing agent, thickener, or mixturethereof, the emulsion having a solids content of from 35 to 80 percentby weight, (B) from 0.2 to 2 parts by weight of lauryl alcohol, (C) from0 to 10 parts by weight of fibers having a diameter of from 1 to 10micrometers and a length of from 30 micrometers to 10 millimeters with alength to diameter ratio of greater than 10 to
 1. 15. An aerosolcontainer whose contents are the composition of claim
 1. 16. Aone-compartment aerosol container whose contents are the composition ofclaim 1.